U.S. patent number 4,454,457 [Application Number 06/388,220] was granted by the patent office on 1984-06-12 for power supply system for a linear motor.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Masayoshi Isaka, Shigeyoshi Koike, Kiyoshi Nakamura.
United States Patent |
4,454,457 |
Nakamura , et al. |
June 12, 1984 |
Power supply system for a linear motor
Abstract
In a linear motor composed of a propelling coil laid on
continuously along a track and a field system mounted on a vehicle
for driving it, the propelling coil of an enormous length is
sectioned into a number of propelling coil units which are
connected alternately to two sets of feeders by means of switches,
the feeder sets being supplied with polyphase currents from
different power converters, respectively. The propelling coil units
are connected in series to one another without any interposed
insulation and sectioned by a number of lead conductors so that
every pair of the adjacent propelling coil units has a common coil
portion shared by them and having a length not smaller than that of
the vehicle. A pair of the polyphase lead conductors connected to
each of the propelling coil units are connected, respectively, to
going feeders and return feeders constituting the set of feeders
through switches. Change-over of power supply between the adjacent
propelling coil units is performed during a period in which the
vehicle is running along the common coil section by closing and
opening the associated switches and controlling power
converters.
Inventors: |
Nakamura; Kiyoshi (Katsuta,
JP), Isaka; Masayoshi (Hitachi, JP), Koike;
Shigeyoshi (Katsuta, JP) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JP)
|
Family
ID: |
14127482 |
Appl.
No.: |
06/388,220 |
Filed: |
June 14, 1982 |
Foreign Application Priority Data
|
|
|
|
|
Jun 19, 1981 [JP] |
|
|
56-95060 |
|
Current U.S.
Class: |
318/135;
310/12.18; 310/12.09; 104/292; 318/105 |
Current CPC
Class: |
B60L
15/005 (20130101); Y02T 10/645 (20130101); B60L
2200/26 (20130101); Y02T 10/64 (20130101) |
Current International
Class: |
B60L
15/00 (20060101); H02K 041/02 () |
Field of
Search: |
;318/135,105,106
;310/12-14 ;104/290,292,294 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Japanese Railway Eng., vol. 19, No. 1, 1979, p. 10 by Kan-ichiro
Kaminishi..
|
Primary Examiner: Dobeck; B.
Assistant Examiner: Evans; A.
Attorney, Agent or Firm: Antonelli, Terry & Wands
Claims
We claim:
1. A power supply system for a polyphase linear motor which
includes a propelling coil disposed continuously along a track and
sectioned into a plurality of propelling coil units for generating
a moving magnetic field to drive a vehicle, comprising plural sets
of feeders, a power converter apparatus connected to said feeders,
a group of switch means arranged for connecting alternately said
plurality of propelling coil units to said plural sets of feeders,
and control means for changing over said switch means sequentially
so that said propelling coil units are successively supplied with
power, as said vehicle travels, wherein
said plurality of propelling coil units are connected continuously
in series to constitute said propelling coil and so defined by lead
conductors that the propelling coil units disposed adjacent to each
other have a common coil portion shared by them, each of said
common coil portion extending for a length not smaller than an
effective length of said vehicle;
each of said plural sets of feeders including a going feeder and a
return feeder for each phase;
said switch means being constituted by first switches connected
between one end of each of said propelling coil units and said
going feeders, respectively, and second switches connected between
the other end of each of said propelling coil units and said return
feeders, respectively; and
said power converter apparatus being so arranged that power supply
to one set of said feeders is changed over to another set of said
feeders when said vehicle is located at a region defined by said
common coil portion to thereby change over the power supply from
one of the adjacent propelling coil units to the other, said
adjacent propelling coil units having said common coil portion
along which said vehicle is running at that moment.
2. A power supply system according to claim 1, wherein said power
converter apparatus includes a number of power converters
corresponding to said plural sets of feeders, respectively.
3. A power supply system according to Claim 1, wherein said power
converter apparatus includes a single power converter and switching
means for exchangeably connecting the output of said power
converter to said plural sets of feeders.
4. A power supply system according to claim 1, wherein said
propelling coil units each provided for each phase are disposed as
offset from one another by a length not smaller than the effective
length of said vehicle, said power converter apparatus including
single-phase power converters in number at least equal to the
number of phases of said linear motor plus one and arranged in such
a manner in which, when said vehicle is located at the region
defined by the common coil portion of a given one of said phases,
power supply from one of said single-phase power converters to the
propelling coil unit of said given phase constituting a part of
said common coil portion is changed over to power supply to the
adjacent propelling coil unit of said given phase constituting the
other part of said common coil portion from another single-phase
power converter which is not activated at that moment.
5. A power supply system according to claim 1, wherein said power
converter apparatus includes a poly-phase thyristor switch unit for
forming a neutral point either for said going feeders or said
return feeders.
6. A power supply system according to claim 1, wherein said power
converter apparatus includes means for instantaneously changing
over the power supply from one set of said feeders to other set of
said feeders, when said vehicle is present at the region defined by
said common coil portion and when the switch means associated with
the adjacent propelling coil units sharing said common coil portion
are in the closed state.
7. A power supply system according to claim 1, wherein said
plurality of propelling coil units are directly connected in series
to one another without interposition of insulation
therebetween.
8. A power supply system according to claim 1, wherein said power
converter apparatus includes means for changing over the power
supply from one of the adjacent propelling coil units to the other
adjacent propelling coil unit with substantially no variation in
the power supplied to the adjacent propelling coil units.
9. A power supply system according to claim 1, wherein said control
means controls the switching of said switching means at a time when
current does not flow therethrough.
Description
The present invention relates in general to a power supply system
for a linear motor. In particular, the invention is directed to an
improvement of a power supply apparatus for a so-called long stator
type linear motor such as a linear synchronous motor and the like
for driving a vehicle, which motor comprises an armature coil (or
propelling coil) laid on along a stationary track of the vehicle
and a field system which is mounted on the vehicle.
There are known various applications of the long stator type linear
motor mentioned above. Above all, application of the long stator
linear motor to the ultra-high speed railway system developed
recently is well known. In the case of the linear synchronous
motor, the armature coil is disposed along the track, while in a
linear induction motor, the primary coil is installed along the
track. In an effort to improve the power supply efficiency, the
armature coil or the primary coil (hereinafter, the long stator
coil installed along the track is referred to as the propelling
coil) is usually divided into sections of an appropriate length,
wherein the sectioned propelling coils are supplied with electric
power from a power converter apparatus (such as inverter and
cyclo-converter, for example) through well known mechanical
switches or static type switches constituted by thyristors, whereby
the vehicle is caused to run along the track under the propelling
force produced through electromagnetic action between the
travelling or moving field generated by the propelling coil and the
field system or reaction plates installed on the body of the
vehicle. There are imposed on the power supply system for the long
stator type linear motor including the divided or sectioned
propelling coils such requirements as mentioned below.
(a) Variation in the propelling force should be suppressed to
minimum when the vehicle runs along a track section defined by the
adjacent propelling coil units.
(b) Variation in power at the input side of the power converter
should be suppressed as small as possible when the vehicle runs
across the adjacent propelling coil units.
(c) The power supply system should be implemented
inexpensively.
As the power supply system for the linear motor which is designed
to meet the requirements mentioned above, there is known for
practical application a power supply apparatus shown in FIG. 1A of
the accompanying drawings (reference is to be made to Japanese
Patent Publication No. 23402/1979, FIG. 9). In the following,
structure and operation of this known power supply system will be
briefly elucidated to thereby make clear the problems to be solved
by the invention.
Referring to FIG. 1A which shows schematically a circuit
arrangement for a single phase of a power supply system for a
three-phase linear motor, reference symbols LM.sub.1, LM.sub.2, . .
. , LM.sub.5 denote, respectively, the divided propelling coil
units which are sequentially connected to feeders F.sub.a and
F.sub.b alternately through switches S.sub.1, S.sub.2, . . . ,
S.sub.5, respectively.
When a vehicle represented by T is at the position shown in the
figure, both the switch S.sub.2 associated with the propelling coil
unit LM.sub.2 at which the vehicle T is located at that moment and
the switch S.sub.3 for the propelling coil unit LM.sub.3
corresponding to the section which the vehicle T is to enter in
succession are closed, whereby the propelling coil unit LM.sub.2 is
supplied with electric power from a power converter C.sub.b. When
the vehicle T begins to enter the section corresponding to the
propelling coil unit LM.sub.3, another power converter C.sub.a
which has been in the standby state is activated to initiate the
power supply to the propelling coil unit LM.sub.3. No sooner the
vehicle T has left the propelling coil unit LM.sub.2 and entered
the region of the propelling coil unit LM.sub.3 completely than the
power converter C.sub.b operated until then is de-activated with
the switch S.sub.2 being opened, while the switch S.sub.4 for the
propelling coil unit LM.sub.4 which the vehicle T is to enter next
is beforehand closed with the power converter C.sub.b being set to
the standby state. The above operations are repeated in the similar
manner to cause the vehicle to run continuously.
With the power supply system described above, the vehicle is
incessantly subjected to a propelling force. Since the two adjacent
propelling coil units across which the vehicle is moving are
supplied with power from the respective power converters C.sub.a
and C.sub.b independent of each other, there will occurs no
variation in the propelling force, to advantage. However, it is
noted that apparent powers P.C.sub.a and P.C.sub.b of power
receiving transformers T.sub.ra and T.sub.rb as well as the total
apparent power P.SS appearing at a power receiving point SS undergo
periodic variations with the total apparent power P.SS being
increased during a period in which both the power converters
C.sub.a and C.sub.b are operated simultaneously, as can be seen
from waveform diagrams illustrated in FIG. 1B. Such variation in
the apparent powers can be explained by the fact that excitation of
the two adjacent propelling coil units involves an increase in the
reactive power.
As approaches for reducing variation in the apparent power which
occurs at the time when the vehicle is running across the two
adjacent propelling coil units, there have been proposed a power
supply system shown in FIG. 2A of the accompanying drawings (also
refer to Japanese Patent Publication No. 32086/1980) and another
power supply system shown in FIG. 3A (reference is to be made to
Japanese Patent Laid-Open No. 18013/1976). In FIGS. 2A and 3A, same
reference symbols are used to denote like or same components as
those shown in FIG. 1. Accordingly, repeated description of the
individual components will be unnecessary.
In the power supply system shown in FIG. 2A, the propelling coil
units positioned adjacent to each other are disposed so as to be
partially superposed each other by a length greater than the
effective length of the vehicle (e.g. total length of the field
system mounted on the vehicle in the case of the linear synchronous
motor). At the time point at which the vehicle comes to be
positioned above the superposed section as is illustrated in FIG.
2, the power converter C.sub.b which has supplied power to the
propelling coil unit LM.sub.2 until then is instantaneously changed
over to the power converter C.sub.a, whereby the vehicle can
receive the propelling force successively from the propelling coil
unit LM.sub.3 without interruption. A power supply switching
control apparatus SC is provided to control the closing and opening
of a group of switches S and the change-over between the power
converters C.sub.a and C.sub.b on the basis of a signal
representative of the position of the vehicle. When the power
converter is constituted by a cyclo-converter or inverter composed
of thyristors, the change-over of the power converters can be
easily accomplished in a manner illustrated by waveform diagrams of
FIG. 2C. More specifically, operation of the power converter
C.sub.b is stopped at the time point at which the polarity of a
current i.sub.LM2 flowing through the propelling coil unit LM.sub.2
is changed, while the power converter C.sub.a is simultaneously
activated to thereby supply a current i.sub.LM3 to the propelling
coil unit LM.sub.3. In case each of the power converters is
composed of thyristors, activation and deactivation of the power
converter can be easily accomplished by applying turn-on and
turn-off signals to the gate electrodes of the thyristors in the
manner well known in the art. Accordingly, the currents supplied to
the propelling coil units LM.sub.2 and LM.sub.3 in succession may
be regarded as being continuous, as can be seen from a current
waveform (i.sub.LM2 +i.sub.LM3) shown in FIG. 2C, involving no
variation in the propelling force acting on the vehicle. Further,
no variation occurs in the receiving apparent power P.SS, as is
illustrated in FIG. 2B. It should here be mentioned that when the
power supply to the propelling coil units is changed over in the
manner mentioned above, it is not always necessary to provide the
power converters in a pair, but provision of a single power
converter will be sufficient by adopting such a circuit arrangement
in which the output power from the single power converter is
coupled alternately to the feeders F.sub. a and F.sub.b by means of
branching switches BS.sub.a and BS.sub.b, the switching of which is
controlled by the aforementioned power supply switching control
apparatus SC, as is shown in FIG. 2D. For more details, reference
is to be made to Japanese Patent Publication No. 32086/1980, FIG.
6A.
However, the power supply systems shown in FIGS. 2A and 2D are
disadvantageous in that the installation of the propelling coils
involves high expenditure and complicated procedures, because the
adjacent coils have to be superposed onto each other by a length
greater than that of the vehicle body.
In an attempt to eliminate the disadvantages of the power supply
systems described above, there is also known a power supply system
shown in FIG. 3A in which a continuous propelling coil is
electrically sectioned into a number of the propelling coil units
LM.sub.1, LM.sub.2, LM.sub.3, LM.sub.4 and so forth by means of
lead-out conductors so that the coil units disposed adjacent to
each other share a common coil portion of a length greater than
that of the vehicle body. When the vehicle is located at the region
corresponding to the common or shared coil portion of the
propelling coil units LM.sub.1 and LM.sub.2, for example, the power
supply is changed over in such a manner in which the coil unit
LM.sub.1 is first energized, being followed by energization of the
propelling coil unit LM.sub.2, as is in the case of the
aforementioned power supply systems.
FIG. 3B shows a power supply circuit realized in a configuration
similar to the one illustrated in FIG. 2A in the assumed case where
the propelling coil is composed of two coil units. At the instant
the vehicle T enters the common coil portion of the two adjacent
propelling coil units LM.sub.1 and LM.sub.2, power supply is
changed over so that the power converter C.sub.a which has been
operated until then is deenergized, while the power converter
C.sub.b is simultaneously activated, as is illustrated by a
single-dot broken line loop. There arise no problems so far as the
number of the propelling coil units as provided is two.
However, the power supply circuit of the type similar to the one
mentioned just above and destined to supply electric power to three
or more propelling coil units, as is in the usual case, suffers a
problem remaining to be solved. A typical example of the power
supply circuit in question is shown in FIG. 3C. Referring to this
figure, it is assumed that the vehicle is currently positioned over
the common coil portion shared by the propelling coil units
LM.sub.1 and LM.sub.2, wherein operation of the power converter
C.sub.a is stopped while operation of the power converter C.sub.b
has just been triggered. In this case, the current fed from the
power converter C.sub.b flows not only along the current path
extending through the propelling coil unit LM.sub.2 as indicated by
a single-dotted broken line but also along a shunting current path
extending through a coil portion of the propelling coil unit
LM.sub.1 at which the vehicle is no more present, as indicated by a
broken line. This means that the current of predetermined magnitude
does not flow through the propelling coil unit at which the vehicle
is present at the moment, eventually decreasing the propelling
force, while loss is increased because of the useless current
flow.
As will be obvious from the above description, when the propelling
coil is electrically divided or sectioned in the manner shown in
FIG. 3A with the propelling coil units and the power converters
being interconnected in the manner shown in FIG. 3C similarly to
the case where power is supplied to the propelling coil units which
are physically and partially superposed onto one another between
the adjacent ones as shown in FIG. 2A, there will arise decreases
and variations in the propelling force to which the vehicle is
subjected.
An object of the present invention is to provide a power supply
system for a long stator linear motor in which a plurality of
propelling coil units are electrically connected in series to one
another in succession and sectioned into the coil units by means of
lead-out conductors and which system is capable of changing over
the power supply in succession to the individual propelling coil
units in a very stable manner without incurring reduction in the
propelling force and other disadvantages due to the aforementioned
shunt current flow.
In view of the above object, there is provided according to an
aspect of the present invention a power supply system for a long
stator linear motor in which a continuous propelling coil is
sectioned into a plurality of propelling coil units by means of
lead-out conductors so that each pair of the propelling coil units
disposed adjacent to each other have a common or shared coil
portion of a length at least equal to that of a vehicle to be
driven by the long stator linear motor and are supplied with
electric power from power converters, and which comprises switch
means each inserted in a current feeding path and a current return
path formed, respectively, between each of the propelling coil
units and each of the power converters so that only the single
propelling coil unit is connected to one of the power converters
without forming any shunt circuit, to thereby solve the problems
brough about by formation of the shunt circuit in the hitherto
known power supply systems described hereinbefore.
The present invention will be apparent from the following detailed
description taken in conjunction with the accompanying drawings, in
which:
FIG. 1A is a circuit diagram showing an example of hitherto known
power supply systems for a long stator linear motor;
FIG. 1B shows waveform diagrams to illustrate operations of the
power supply system shown in FIG. 1A;
FIG. 2A shows in a circuit diagram another example of the hitherto
known power supply systems for the long stator linear motor;
FIGS. 2B and 2C show waveform diagrams to illustrate operations of
the power supply system shown in FIG. 2A;
FIG. 2D shows in a circuit diagram a modification of a circuit
portion including power converters in the power supply system shown
in FIG. 2A;
FIGS. 3A and 3B are circuit diagrams showing still another example
of the hitherto known long stator linear motor system;
FIG. 3C shows a circuit diagram of a power supply system for the
long stator linear motor shown in FIGS. 3A and 3B to elucidate the
problems which the power supply system suffers;
FIG. 4A is a schematic circuit diagram showing a circuit
arrangement for one phase of a power supply system for a
three-phase long stator linear motor to illustrate the principle of
the present invention;
FIG. 4B shows waveform diagrams to illustrate operations of the
power supply system shown in FIG. 4A;
FIG. 5 shows schematically a circuit arrangement of the power
supply system of FIG. 4A for all the three phases;
FIGS. 6A and 6B show circuit arrangements of a power converter
which can be employed in the power supply system shown in FIG. 5A
according to an exemplary embodiment of the invention;
FIG. 7A is a schematic circuit diagram of the power supply system
for a long stator linear motor according to another embodiment of
the invention;
FIG. 7B shows waveform diagrams to illustrate operations of the
power supply system of the linear motor shown in FIG. 7A;
FIG. 8A shows in a schematic circuit diagram still another
embodiment of the power supply system for the long stator linear
motor according to the invention; and
FIG. 8B shows waveform diagrams to illustrate operations of the
system shown in FIG. 8A.
Now, exemplary embodiments of the present invention will be
described in detail by first referring to FIG. 4A which
schematically shows a general circuit configuration of the power
supply system for a long stator linear motor according to an
embodiment of the invention to illustrate the principle thereof and
FIG. 4B showing waveform diagrams to illustrate operations of the
power supply system shown in FIG. 4A.
Referring to FIG. 4A in which the power supply circuit is shown for
one phase of a three-phase long stator linear motor, a propelling
coil which constitutes the long stator of the linear motor and laid
on along a track of a vehicle driven by the linear motor is
sectioned into a plurality of propelling coil units LM.sub.1,
LM.sub.2, LM.sub.3 and so forth by means of lead conductors in such
a manner that the propelling coil units located adjacent to each
other have in common a coil portion which is shared by (CCP.sub.12,
CCP.sub.23 and so forth) them and has a length not smaller than an
effective length of the 1 vehicle. The lead conductors are
connected to feeders through respective switches. More
specifically, in the case of the illustrated example, the
propelling coil units denoted by attaching odd-numbered suffixes,
i.e. LM.sub.1, LM.sub.3 and so forth, have one lead conductors
connected to the feeder F.sub.a through switches S.sub.1, S.sub.3
and so forth, respectively, and other lead conductors connected to
the feeder NF.sub.a through switches NS.sub.1, NS.sub.3 and so
forth, respectively. On the other hand, the even-numbered
propelling coil units LM.sub.2, LM.sub.4 and so forth have one lead
conductors connected to the feeder F.sub.b through switches
S.sub.2, S.sub.4 and so forth, respectively, and other lead
conductors connected to the feeder NF.sub.b through switches
NS.sub.2, NS.sub.4 and so forth, respectively. The odd-numbered
propelling coil units LM.sub.1, LM.sub.3 and so forth are adapted
to be supplied with electric power from a power converter C.sub.a,
while the even-numbered propelling coil units are energized by a
power converter C.sub.b. Activation and deactivation of the power
converters C.sub.a and C.sub.b as well as alternate turn-on/off of
the switches S.sub.1 ; NS.sub.1, S.sub.2 ; NS.sub.2 and so forth
are controlled by a power supply switching controller SC in
dependence on the instantaneous position of the vehicle. Operations
of the power supply system shown in FIG. 4A will be described below
with the aid of the waveform diagrams shown in FIG. 4B.
Referring to FIG. 4A, it is first assumed that the vehicle denoted
generally by a reference letter T is located at a position
represented by T.sub.1. In this state, the switches S.sub.1 and
NS.sub.1 of the propelling coil unit LM.sub.1 have already been
closed, whereby the vehicle T is being driven under the propelling
force exerted by the propelling coil unit LM.sub.1 being at the
moment energized by the power converter C.sub.a. Here, it should be
noted in conjunction with the signal waveform diagrams labelled
with S.sub.1, NS.sub.1, etc. that high level of a signal represents
the closed or "ON" state of the associated switch, while the low
level represents the opened or "OFF" state of the same. The
switches S.sub.2 and NS.sub.2 of the propelling coil unit LM.sub.2
to be energized in succession are in the closed or "ON" state,
while the power converter C.sub.b is deactivated and thus is in the
standby state ready for being activated. The switches for all the
other coil units are in the "OFF" state.
During a period in which the vehicle T is running along the common
coil portion or section shared by two given adjacent propelling
coil units, e.g. from the vehicle position T.sub.1 at which the
vehicle T has completely entered the section corresponding to the
coil unit LM.sub.2 to the position T.sub.2 immediately before the
vehicle begins to leave or exit from the propelling coil unit
LM.sub.1, as shown in FIG. 4A, the power converter C.sub.a is
deactivated, while the power converter C.sub.b is activated
simultaneously with the deactivation of the converter C.sub.a, to
thereby change over the power supply to the propelling coil unit
LM.sub.2 from the coil unit LM.sub.1 at a time point denoted by x
in FIG. 4B. It is most desirable that the above mentioned
change-over of the power supply between the adjacent propelling
coil units be effected at zero current points with a view to
suppressing variations in the propelling force as well as transient
variations in power to the possible minimum, as described
hereinbefore in conjunction with FIG. 2C.
After the change-over of the power supply mentioned above, the
power converter C.sub.a remains deactivated until the next
change-over operation. Accordingly, during a period in which the
power converter C.sub.a is deactivated, the switches S.sub.1 and
NS.sub.1 which have been closed until then are opened, while the
switches S.sub.3 and NS.sub.3 of the propelling coil unit LM.sub.3
which the vehicle T is to enter in succession are closed to thereby
prepare the power supply path or circuit for the propelling coil
unit located in succession as viewed in the travelling direction of
the vehicle T at a time point y shown in FIG. 4B. However, the
switching (i.e. opening and closing) of the associated switches may
be effected only before the succeeding change-over of the power
supply is to take place. The opening and closing of all these
switches can be effected in the no-current state. In this
connection, it is preferred that the opening of the switches
S.sub.1 and NS.sub.1 or more generally S.sub.i and NS.sub.i where i
is a given integer would be effected at different time points for
the reason mentioned below. Since these switches S.sub.i and
NS.sub.i are opened after the operation of the power converter
C.sub.a has been stopped, it may appear that the opening of these
switches S.sub.i and NS.sub.i at different time points would be
meaningless. However, consideration should also be paid to the fact
that these switches might be opened in the current flowing state
due to failures in the controller or for other causes. In such
case, both of the switches S.sub.i and NS.sub.i must have a
capability of breaking the load current, when they are to be opened
simultaneously. Under the circumstances, it is desirable that
either of the switch S.sub.i or NS.sub.i be opened in precedence to
the other, because then only one of the switches S.sub.i and
NS.sub.i needs to be imparted with the load current breaking
capability (i.e. the capability of breaking the load current upon
occurrence of failure, even if it is rare), while the other switch
need not have such capability. Then, the burden imposed on the
switches S.sub.i and NS.sub.i can be balanced as a whole, whereby
not only the costs required for these switches can be remarkably
reduced but also the reliability as well as facility of maintenance
of the switch system can be enhanced significantly.
When the vehicle T comes to a position T.sub.3 at which the vehicle
T has entered a region corresponding to the common coil portion
shared by the propelling coil units LM.sub.2 and LM.sub.3, the
power supply is changed over from the coil unit LM.sub.2 to the
coil unit LM.sub.3, while the current feeding paths to the
succeeding propelling coil unit LM.sub.4 as viewed in the traveling
direction of the vehicle T is prepared by opening and closing the
associated switches in the manner described above. Similar
procedure is repeated to cause the vehicle to run continuously. It
will be seen from FIG. 4B that the input apparent powers P.C.sub.a
and P.C.sub.b of the power converters C.sub.a and C.sub.b are such
as represented by the signal waveforms P.C.sub.a and P.C.sub.b,
respectively, resulting in that the total apparent power, that is
the apparent power P.SS received by the whole power converter
apparatus PS scarcely undergoes variation, as can be seen in the
signal waveform P.SS in FIG. 4B.
In this way, when the propelling coil unit LM.sub.3, for example,
is being supplied with power through the power converter C.sub.a,
the switch NS.sub.1 inserted in the current return path of the coil
unit LM.sub.3 has been opened (in reality, this switch NS.sub.1 was
opened at the time point when the propelling coil unit LM.sub.1 had
been deenergized). Accordingly, there can be positively excluded
the possibility of such a shunt current path as indicated by the
broken line loop in FIG. 3C being formed extending through a part
of the other propelling coil unit at which the vehicle is not
present.
Of course, it goes without saying that the switches S.sub.i and
NS.sub.i can be closed and opened in the no-current state.
As described hereinbefore, FIG. 4A shows the power supply circuit
arrangement for the only one phase. In practice, the power supply
circuit may be realized in such a configuration as shown in FIG. 5
for a three-phase linear motor. In FIG. 5, the propelling coils
LMU, LMV and LMW each provided for each phase of the three-phase
system are depicted in thick solid lines. The switches, the feeders
and the power converters are provided so as to correspond with the
three-phase system. Arrangement of these components for the one
phase is identical with what is shown in FIG. 4A.
FIG. 6A shows an exemplary arrangement of the three-phase power
converter circuit for the three-phase system shown in FIG. 5. The
power converter circuit shown in FIG. 6A is composed of a
three-phase cyclo-converter C constituted by three single-phase
cyclo-converters C.sub.U, C.sub.V and C.sub.W and has one output
terminals connected to the feeders F and the other connected to the
feeders NF, to thereby provide the power supply source circuit for
the three-phase linear motor.
In contrast to FIG. 6A, FIG. 6B shows an exemplary power supply
converter circuit in which a conventional three-phase inverter INV
having no neutral point is made use of as the power converter. In
this case, it is required to provide a thyristor switch circuit TS
which can be turned on and off in synchronism with activation and
deactivation of the three-phase inverter INV for the purpose of
providing a neutral point for the three-phase propelling coil
units. More particularly, in the case of the power supply systems
described hereinbefore in conjunction with FIGS. 1A and 2A, the
neutral point of the propelling coil units in the three-phase
connection can be formed without any difficulty merely by
connecting the current return paths of these three-phase propelling
coil units directly to the current return feeder without inserting
the return path switches NS shown in FIG. 4A. However, it will
readily be understood from the three-phase power supply circuit
diagram shown in FIG. 5 that the mere connection of all the feeders
NF for the current return paths at a single point will give rise to
a problem mentioned below. Namely, assuming that the power supply
is changed over from the propelling coil unit LM.sub.3 to the
LM.sub.4 during a period in which the vehicle T is running along
the common coil portion shared by these coil units LM.sub.3 and
LM.sub.4, then the switches NS.sub.3, S.sub.4 and NS.sub.4 (not
shown) are closed while all the other switches are opened. Up to a
time point immediately before the power supply is to be changed
over as described above, the propelling coil unit LM.sub.3 is
energized by way of a current path which extends from the power
converter C.sub.A to the neutral point located within it through
the switch S.sub.3, the propelling coil unit LM.sub.3 and the
return path switch NS.sub.3. Starting from this state, the power
supply is transferred to the propelling coil unit LM.sub.4 by
activating the power converter C.sub.B while deactivating the
converter C.sub.A. However, since the neutral point is formed
within the power converter which is connected to the return path
switch unit NS.sub.3, the current supplied from the power converter
C.sub.B will flow through a local current path extending from the
converter C.sub.B to the neutral point within it through a part of
the propelling coil unit LM.sub.4 and the return path switch
NS.sub.3 instead of flowing through the whole propelling coil unit
LM.sub.4 in the case where the three phases are combined together
at the single point. For the current to be caused to flow through
the whole propelling coil unit LM.sub.4 by any means, it is
required to open the return path switch NS.sub.3, which in turn
means that the return path switch NS.sub.3 has to be imparted with
the current breaking capability and that the propelling force
acting on the vehicle undergoes variation in correspondence to the
variation in the current flowing through the propelling coil unit
LM.sub.4. In the light of the above, it is desirable to form the
neutral point by using the thyristor switch unit TS when the
conventional three-phase inverter having no neutral point is
employed as the power supply converter for the three-phase linear
motor system. In this case, when the power supply is to be changed
over from the propelling coil unit LM.sub.3 to LM.sub.4, the power
converter C.sub.A is deactivated by applying a turn-off signal to
the inverter INV and the gate of the thyristor switch unit TS while
the power converter C.sub.B is activated by applying a turn-on
signal to the associated inverter INV and the gate of the thyristor
switch. Since the power converter C.sub.A is opened at the side
connected to the return path switch NS.sub.3, the current supplied
from the power converter C.sub.B can flow along a path extending
from the inverter INV of the power converter C.sub.B through the
switch S.sub.4, the propelling coil unit LM.sub.4 and the return
path switch NS.sub.4 (not shown) to the thyristor switch TS of the
power converter C.sub.B.
FIG. 7A shows another embodiment of the invention in which coil
sections constituting the three-phase propelling coil unit are
positionally shifted or offset from one another for U-, V- and
W-phases. It is known from the Japanese Patent Publication No.
14603/1980 that the power supply system for a three-phase linear
motor is so constituted that the phase coil sections of each of the
propelling coil units are positionally shifted or offset from one
another for the purpose of decreasing the number of the individual
thyristor power converters which constitute the power converter
apparatus. In the case of the embodiment shown in FIG. 7A, the
teaching disclosed in the above cited Japanese Patent Publication
is applied to the power supply system for the propelling coil units
connected in series as shown in FIG. 5. Now, description of the
power supply system shown in FIG. 7A will be made in detail.
The propelling coil units LMU.sub.n, LMV.sub.n and LMW.sub.n
belonging to the n-th coil section of the propelling coils LMU, LMV
and LMW of a three-phase linear motor are disposed as offset from
one another by a length not smaller than the effective length of a
vehicle to be driven by the three-phase linear motor, wherein the
propelling coil units located adjacent to each other in the same
phase propelling coil such as LMU.sub.n and LMU.sub.n+1, for
example, are so defined or sectioned by means of the lead wires
that a coil portion of a length greater than the effective length
of the vehicle is shared in common between these adjacent coil
units of the same phase. The propelling coil units LMU.sub.n,
LMV.sub.n, LMW.sub.n, LMU.sub.n+1 and so forth have one lead
conductors connected sequentially and repeatedly to four going or
incoming feeders F.sub.a, F.sub.b, F.sub.c and F.sub.d through
switches SU.sub.n, SV.sub.n, SW.sub.n, SU.sub.n+1 and so forth,
respectively, and other lead conductors connected sequentially and
repeatedly to four return feeders NF.sub.a, NF.sub.b, NF.sub.c and
NF.sub.d through the switches NSU.sub.n, NSV.sub.n, NSW.sub.n,
NSV.sub.n+1 and so forth, respectively. The four sets of the
feeders (F.sub.a ; NF.sub.a), (F.sub.b ; NF.sub.b), (F.sub.c ;
NF.sub.c) and (F.sub.d ; NF.sub.d) each for one phase are connected
to four power converters C.sub.a, C.sub.b, C.sub.c and C.sub.d each
for one phase, respectively.
Describing operations of the power supply system shown in FIG. 7A
by also referring to the signal waveform diagrams shown in FIG. 7B,
it is assumed that the vehicle T is located at the section
corresponding to the common portion shared by the adjacent
propelling coil units LMU.sub.n and LMU.sub.n+1, as is shown in
FIG. 7A. On the assumption, the switches are at the positions
indicated by solid line bars, wherein the propelling coil unit
LMU.sub.n of U-phase above which the vehicle is present at the
moment is electrically energized from the power converter C.sub.a
through the switches SU.sub.n and NSU.sub.n, while the propelling
coil unit LMV.sub.n of the V-phase is supplied with power from the
power converter C.sub.b through the switches SV.sub.n and
NSV.sub.n, and the propelling coil unit LMW.sub.n of the W-phase is
powered from the power converter C.sub.c through the switches
SW.sub.n and NSW.sub.n. In this state, the switches SU.sub.n+1 and
NSU.sub.n+1 of the propelling coil unit LMU.sub.n+1 to be supplied
with power in succession have been already closed (after the
preceding change-over of power supply). However, the power
converter C.sub.d is not yet operated but in the standby state
ready for being activated. When the power converter C.sub.a is
deactivated with the power converter C.sub.d being activated
starting from this state in the manner described hereinbefore in
conjunction with FIG. 2C, the power supply can be changed over
smoothly from the propelling coil unit LMU.sub.n to the coil unit
LMU.sub.n+1, whereby the vehicle can be driven or propelled
continuously and smoothly.
In the new state mentioned just above, the power converter C.sub.a
is deactivated, while the power converters C.sub.b, C.sub.c and
C.sub.d supply electric power to the propelling coil units
LMV.sub.n, LMW.sub.n and LMU.sub.n+1, respectively. The next
change-over of the power supply to be effected as the vehicle
travels is from the propelling coil unit LMV.sub.n to the coil unit
LMV.sub.n+1. To this end, the switches SU.sub.n and NSU.sub.n are
opened while the switches SV.sub.n+1 and NSV.sub.n+1 are closed as
indicated by broken lines in FIG. 7A to thereby allow the
connection of the deactivated power converter C.sub.a to be changed
over from the propelling coil unit LMU.sub.n of the U-phase to the
V-phase propelling coil unit LMV.sub.n+1 (not shown).
In this way, the idle one of the four power converters is
successively connected to the propelling coil units which come
successively to the position to be immediately occupied by the
travelling vehicle and which belongs to the phase of which the
power supply is to be changed over. Changing-over of the various
power converters as well as opening and closing of the associated
switches mentioned above take place successively and repeatedly, as
the vehicle travels, in the manner illustrated by the waveform
diagrams shown in FIG. 7B, whereby the vehicle is allowed to run
continuously and smoothly along the track defined by the
three-phase propelling coil units connected in series and having
three phase coil sections positionally shifted or offset relative
to one another in the traveling direction of the vehicle. In
connection with FIG. 7B, it should be added that an expression (SU,
NSU).sub.n, for example, represents the switches SU.sub.n and
NSU.sub.n in combination which serve to connect the U-phase
propelling coil unit LMU.sub.n of the n-th section to the feeders
and that high level of the signal waveform represents the closed
state of the associated switches, while the low level represents
the opened state of the associated switches. On the other hand, the
waveforms P.C.sub.a, . . . , P.C.sub.d represent the operating
states of the power supply converters C.sub.a, . . . , C.sub.d,
respectively, wherein the high level means that the concerned power
converter is in the power supplying state, while the low level
means that the converter is deactivated. Further, the reference
letters LMU.sub.n, LMV.sub.n, LMW.sub.n and so forth inserted in
the waveform diagrams P.C.sub.a, . . . , P.C.sub.d, respectively,
denote the propelling coil units which are being supplied with
power from the power converters C.sub.a, . . . , C.sub.d,
respectively. The abscissa represents positions of the track.
Finally, the waveform curve P.SS represents the total apparent
power of all the four power converters at the input side thereof.
As will be seen, no variation occurs in the total apparent
power.
As will be appreciated from the above description, the three-phase
power supply system illustrated in FIGS. 7A and 7B makes it
possible to supply power to the three-phase propelling coil units
alternately exchangeably without any appreciable variations in the
power being supplied with the aid of as small a number as of four
single-phase power converters.
FIG. 8A shows another exemplary embodiment of the invention in
which there is adopted a system for selectively and exchangeably
conducting the output power of a single power converter by means of
thyristor switches as shown in FIG. 2D is adopted. Referring to
FIG. 8A, the power converter circuit PS is composed of a single
three-phase power converter C, thyristor switches (BSU.sub.A ;
BSU.sub.B), (BSV.sub.A ; BSV.sub.B) and (BSW.sub.A ; BSW.sub.B) for
conducting the output power of the three-phase power converter C to
the going feeders F.sub.A and F.sub.B, and thyristor switches
(BNSU.sub.A ; BNSU.sub.B), (BNSV.sub.A ; BNSV.sub.B) and
(BNSW.sub.A ; BNSW.sub.B) for conducting the output power of the
three-phase converter C to the return feeders NF.sub.A and
NF.sub.B. With such circuit arrangement, operations of the switches
are effected in a similar manner as is in the case of the
embodiment shown in FIGS. 4A and 5A. Change-overs between the
thyristor switches between (BSU.sub.A ; BNSU.sub.A) and (BSU.sub.B
; BNSU.sub.B), between (BSV.sub.A ; BNSV.sub.A) and (BSV.sub.B ;
BNSV.sub.B) and between (BSW.sub.A ; BNSW.sub.A) and (BSW.sub.B ;
BNSW.sub.B) may be realized in a manner similar to the change-over
between the power converters C.sub.A and C.sub.B shown in FIG. 5.
FIG. 8B shows waveform diagrams to illustrate change-over operation
for the U-phase. Assuming now that the vehicle has completely
entered the common coil portion shared by the adjacent propelling
coil units, the gates of the thyristor switches BSU.sub.A and
BNSU.sub.A which have been conducting until then are turned off at
a time point a shown in FIG. 8B, while the gates of the thyristors
BSU.sub.B and BNSU.sub.B (referred to as forward thyristors for
convenience's sake) connected with a polarity opposite to that of
the output current of the power converter C (the polarity of the
output current is negative in the case of the illustrated
embodiment) are turned on. At a time point b at which the polarity
of current is inverted, the change-over of the power supply takes
place. More concretely, the thyristor switches BSU.sub.A and
BNSU.sub.A whose gates are turned off become spontaneously
non-conductive upon inversion of the current polarity, whereby the
output current of the power converter C is changed over toward the
thyristor switches BSU.sub.B and BNSU.sub.B. Thereafter, the gates
of these backward thyristors BSU.sub.B and BNSU.sub.B are turned on
at a time point C. When the change-over among the thyristor
switches for the U-, V- and W-phases have been completed, the
switches S.sub.i and NS.sub.i (e.g. S.sub.3 and NS.sub.3 in the
case of the illustrated embodiment) which have been closed until
then are opened, while the switches (e.g. S.sub.5 and NS.sub.5 not
shown) for the propelling coil units which have to be next
energized for driving the vehicle are closed. In this manner, the
change-over of the power supply to the three-phase propelling coil
units are repeatedly performed as the vehicle travels further.
With the circuit arrangement shown in FIG. 8A, installation of a
single power converter is sufficient for attaining the desired
power supply operation in the three-phase power supply system,
although provision of the thyristor switches are required.
As will be appreciated, there has been provided according to the
present invention the power supply system for the long stator
linear motor in which no current shunting path is formed when the
power supply is changed over from one to another sectioned
propelling coil units and in which the receiving or input power
undergoes substantially no variations when the vehicle is running
along the common coil portion shared by every adjacent propelling
coil units. Thus, the power supply system for the linear motor
according to the invention can assure comfortable ride in the
vehicle with reduced expensiveness.
* * * * *